Martin Hessling

In Situ Measurement of Tropospheric OH Radicals by Laser-Induced Fluorescence—A Description of the KFA Instrument

Abstract An instrument for the measurement of tropospheric OH radical concentrations by laser-induced fluorescence spectroscopy has been developed. Ambient air is expanded through a nozzle into a low-pressure fluorescence cell and is irradiated by a frequency-doubled dye laser, which is pulsed with a high repetition rate of 8.5 kHz. The laser wavelength is tunable to selectively excite single rovibronic transitions of the OH radicals at 308 nm [A2∑+(ν′ = 0) ← X2 Π (ν″=0)]. The OH resonance fluorescence, emitted mostly between 307 and 311 nm, is detected by gated photon counting. From laboratory calibrations and ambient air measurements the authors infer a detection limit (S/N = 2) of 8 × 105 OH cm−3 for 1-minute data integration time. First tests of the new instrument in ambient air revealed the existence of an interference problem due to generation of OH by a dark reaction of ozone inside the detection cell. Improvements of the instrument reduced the spurious OH signal to a level corresponding to an ambi...

In-line monitoring of Saccharomyces cerevisiae fermentation with a fluorescence probe: new approaches to data collection and analysis

Fluorescence analysis, in particular two‐dimensional excitation‐emission matrix (EEM) spectroscopy, is a sensitive in‐line process monitoring tool in the biotechnological production. Before it can be widely adopted by the industry, fast effective algorithms for the analysis of massive and complex fluorescence data should be developed. Weak emission signals are prone to various interferences complicating the modeling, such as excitation light Rayleigh scatter. The scatter is usually considered as an unwanted background to be avoided or removed.

An extraocular non-invasive transscleral LED-endoilluminator for eye speculum integration

PurposeConventional chandelier-endoilluminators used for pars-plana vitrectomy consist of a light-emitting tip attached to an optical fibre. The tip requires introduction into the ocular space through an incision. To achieve complete illumination of the intraocular space, the introduction of more than just one tip is sometimes necessary. An extraocular vitreoretinal LED-endoilluminator discussed in this paper represents a new approach to illuminate the intraocular space. The light source is integrated into a speculum and firmly apposed to the sclera. This approach offers the advantage of effectively illuminating the interior of the eye even though the procedure is non-invasive. Furthermore, this approach significantly reduces the risk of damage to the retina by phototoxic effects.MethodsA round white LED was used as a light source. By integrating the light source into a speculum, the LED was firmly held against the sclera. Thus, the ocular space was illuminated transsclerally. As a result, indirect uniform illumination of the complete intraocular space was achieved. The prototype was developed considering the relevant international standards. Porcine eyes were used because their properties are similar to those of human eyes.ResultsPorcine eyes could be acceptably illuminated with the selected LED. The LED-endoilluminator conforms with international standards for endoillumination. Thus, possible photochemical and thermal risks are considered and reduced to a minimum.ConclusionsA novel LED-endoilluminator which can be attached to a speculum was developed. The system does not need any connection to an external light source and, consequently, also avoids usage of an optical fibre. Regular and uniform illumination of the intraocular space was achieved by transmitted and scattered visible irradiation, avoiding an incision. The duration of potential light exposure, compared to existing illumination systems, can be significantly increased. This is also true when the illuminator is not directly placed over the pars-plana and the distance to the retina is reduced. Only a part of the light reaches the retina and the fraction of short wavelength becomes very small. Increased safety of the system results from now being able to increase the exposure time and reduce phototoxic stress to the retina.

Fluorescence measurements on nanotiter plates

Two different highly sensitive and fast but low-cost instruments for fluorescence measurements on nanotiter plates or other high density sample arrays are presented. Both instruments use 635 nm diode lasers for the detection of Cy5 fluorescence. In the first device all cavities of the nanotiter plate are illuminated simultaneously and the fluorescence is detected spatially resolved by a charge-coupled device camera within a few seconds. The second system uses an on-chip microscanner for the sequential illumination of the samples and the fluorescence is detected by a simple photomultiplier tube. Both instruments have originally been developed for environmental analysis by immunochemical labeling but they can also be used for other medical and biological purposes where analyte concentrations have to be determined.

Improved contact lens disinfection by exposure to violet radiation

BACKGROUND Conventional procedures for contact lens disinfection, based on solutions with aggressive chemical ingredients, not only affect microorganisms but operate likewise damaging towards the epithelial eye surface. OBJECTIVE The aim of this study was to evaluate the applicability of an alternative or complementary disinfection procedure for contact lenses based on irradiation within the visible wavelength range. METHODS Suspensions of S. auricularis, B. subtilis and E. coli were exposed to 405 nm irradiation, for determining the disinfection efficacy. Surviving rates were analyzed by membrane filtration as well as a semi-quantitative analysis using DipSlides. RESULTS A significant antibacterial effect of the 405 nm irradiation is verifiable for all probed bacteria. Using S. auricularis, there has been no colony forming after an irradiation exposure of 2 hours. CONCLUSION The hitherto existing results give reason for the assumption that violet LEDs integrated in contact lens cases will provide a subsidiary disinfection activity and maybe even offer the reduction of chemical ingredients in lens cleaning solutions to become gentler to the eye. In addition the danger of a rerise of the germ concentration after the completion of the disinfection procedure will be reduced.

Visible optical radiation generates bactericidal effect applicable for inactivation of health care associated germs demonstrated by inactivation of E. coli and B. subtilis using 405-nm and 460-nm light emitting diodes

The Ulm University of Applied Sciences is investigating a technique using visible optical radiation (405 nm and 460 nm) to inactivate health-hazardous bacteria in water. A conceivable application could be point-of-use disinfection implementations in developing countries for safe drinking water supply. Another possible application field could be to provide sterile water in medical institutions like hospitals or dental surgeries where contaminated pipework or long-term disuse often results in higher germ concentrations. Optical radiation for disinfection is presently mostly used in UV wavelength ranges but the possibility of bacterial inactivation with visible light was so far generally disregarded. One of the advantages of visible light is, that instead of mercury arc lamps, light emitting diodes could be used, which are commercially available and therefore cost-efficient concerning the visible light spectrum. Furthermore they inherit a considerable longer life span than UV-C LEDs and are non-hazardous in contrast to mercury arc lamps. Above all there are specific germs, like Bacillus subtilis, which show an inactivation resistance to UV-C wavelengths. Due to the totally different deactivation mechanism even higher disinfection rates are reached, compared to Escherichia coli as a standard laboratory germ. By 460 nm a reduction of three log-levels appeared with Bacillus subtilis and a half log-level with Escherichia coli both at a dose of about 300 J/cm². By the more efficient wavelength of 405 nm four and a half log-levels are reached with Bacillus subtilis and one and a half log-level with Escherichia coli also both at a dose of about 300 J/cm². In addition the employed optical setup, which delivered a homogeneous illumination and skirts the need of a stirring technique to compensate irregularities, was an important improvement compared to previous published setups. Evaluated by optical simulation in ZEMAX® the designed optical element provided proven homogeneity distributions with maximum variation of ± 10 %.

Miniature LED endoilluminators for vitreoretinal surgery

Two innovative approaches for intraocular illumination during vitreoretinal surgery by application of white LEDs are being developed. Both techniques are less harmful to the patient, more convenient for the surgeon and smaller and cheaper compared to conventional illumination by Xenon light sources and optical fibers. These two novel approaches are: I) The miniature LED chandelier endoilluminator consisting of a single white LED with a “light probe” on top of the LED housing that fits in a small incision in the wall of the eye. II) The alternative transscleral LED endoilluminator is integrated into an eye speculum that presses the flat LED top against the eye. The intraocular space is only illuminated by light transmitted through the sclera. In contrast to conventional illumination techniques for vitreoretinal surgery no incision is necessary. Both approaches are evaluated with regard to potential photochemical and thermal risks for the patient´s retina and they are tested on porcine eyes.

Photoinactivation of Legionella rubrilucens by visible light

In this study, the photoinactivation of Legionella by visible light is investigated. The success of this approach would offer new prospects for technical water disinfection and maybe even for therapeutic measures in cases of Legionella infections. Therefore, Legionella rubrilucens was dispensed on buffered charcoal yeast extract medium agar plates and illuminated with different doses of violet light generated by 405 nm light-emitting diodes (LEDs). A strong photoinactivation effect was observed. A dose of 125 J/ cm2 reduced the bacterial concentration by more than 5 orders of magnitude compared to Legionella on unirradiated agar plates. The necessary dose for a one log-level reduction was about 24 J/cm2. These results were obtained for extracellular L. rubrilucens, but other Legionella species may exhibit a similar behavior.

Environmental analysis by laser-induced fluorescence detection on nano titer plates

A small, fast and low cost device for the measurement of analyte concentrations on nano titer plates is desired. By immuno chemical labelling with dyes these analyte concentrations can be determined by laser induced fluorescence detection. A first highly sensitive instrument for fluorescence excitation and detection has been developed. It is based on a diode laser and a CCD camera. Further reduction in price and size is leading to a second system that uses a micro scanner for the sequential illumination of the NTP. The development of this second instrument is still in progress.

New illuminations approaches with single-use micro LEDs endoilluminators for the pars plana vitrectomy

The illumination of the intraocular space during pars plana vitrectomy always bears the risk of retina damage by irradiation. Conventional illumination systems consist of an external light source and an optical fiber to transfer the visible light (radiation) into the eye. Often xenon arc and halogen lamps are employed for this application with some disadvantageous properties like high phototoxicity and low efficiency. Therefore, we propose to generate the light directly within the eye by inserting a white micro LED with a diameter of 0.6 mm. The LED offers a luminous flux of 0.6 lm of white light with a blue peak @ 450 nm and a yellow peak @ 555 nm. The presented prototypes fit through a standard 23 G trocar and are the first intraocular light sources worldwide. Two different single-use approaches have already been developed: a handguided and a chandelier device. The hand-guided applicator enables a directly navigation and illumination up to a working distance of 6 mm. The chandelier device is much smaller and does not need an active navigation of the light cone. The brightness and homogeneity of the illumination of these LED devices have been successfully tested on porcine eyes. Presented measurements and calculations prove that even for high LED currents and small distances to the retina these intraocular micro LED devices expose the retina to less hazard than conventional illumination sources like fiber based xenon systems. Even under the worst circumstances application durations of 180 hours would be justifiable.